1. Field of the Invention
The present invention relates to a device for transferring a lens in use for an optical device, and more particularly, a lens transfer device with a simple structure of drive mechanism, by which a miniaturization design can be enabled, power loss related with lens transfer can be minimized and a lens can be transferred more precisely and stably.
2. Description of the Related Art
In general, an optical instrument has a lens transfer device for transferring a lens by using a cam, screw, motor or piezoelectric element. The lens transfer device uses the motor or piezoelectric element as means for generating driving force and the cam or screw for delivering the driving force.
Accordingly, the lens transfer device is adapted to enable a zooming or focusing function by transferring the lens and thus changing the relative distance of the lens.
FIG. 1 shows a zoom lens barrel for transferring a lens by using a cam, disclosed by U.S. Pat. No. 6,268,970.
According to U.S. Pat. No. 6,268,970 above, a group of lenses 12a, 14a and 16a are transferred along cam curves formed on barrels 12, 14 and 16 to maintain relative distances corresponding to zoom or focal lengths.
In operation of this structure, the relative locations of the lenses 12a, 14a and 16a are easily determined according to the configuration of the cam curves, and an electromagnetic motor is used as a driving source. Here, a zoom lens barrel 10 is adapted to convert rotational motion of the barrel made along the cam curve into a linear motion by using a plurality of deceleration gears, and thus its structure is sophisticated.
Since the lens transfer device as above has a plurality of deceleration gears, it is difficult to miniaturize it. Furthermore, the electromagnetic motor of the lens transfer device consume a large amount of power and generates electromagnetic waves harmful to the human body as well. In addition, it is difficult to transfer the lens with high precision.
FIG. 2 shows a zoom lens mechanism of a camera designed to transfer a lens with screws.
That is, a stationary lens group 22a is combined to a camera body 22, in the object side, and a receiving space is provided in the interior. In the receiving space, an electromagnetic motor 24 is installed, and a guide screw 24a is combined to a shaft of the motor 24.
A power transmission member 26 is engaged on the outer periphery of the guide screw 24a, and a lens barrel 28 is combined to a portion of the power transmission member 26.
In addition, a movable lens group 28a is combined to the lens barrel 28, which is transferred along an optical axis by a guide shaft 29, which is combined along the optical axis inside the camera body 22.
Accordingly, as the motor 24 is actuated, the guide screw 24a rotates, transferring the power transmission member 26 along the optical axis. As the power transmission member 26 is transferred along the optical axis, the barrel 28 is guided by the guide shaft 29 also along the optical axis, enabling a zooming function.
However, the zoom lens mechanism of this camera also uses an electromagnetic motor and thus needs a plurality of deceleration gears, which in turn hinders miniaturization. Furthermore, it is difficult to clear electromagnetic waves generating from the motor or to transfer the lens with high precision.
FIGS. 3a and 3b show a driving device 30 for transferring a lens by using piezoelectric elements in order to overcome problems related with the above described mechanisms.
That is, piezoelectric actuators 32 are fixed to a base block 34 to transfer displacement to driving rods 36, thereby transferring lenses L1 to L4 by using a pressing force of slidable projections 38a and a force of inertia and acceleration effect of a lens frame 38. With this structure, the driving rods 36 can transfer the lens frames 38 or slide inside the projections 38a according to waveforms of input voltages, thereby transferring the lens in both directions.
Electromagnetic waves are not generated since the driving device 30 does not use an electromagnetic motor. The driving device 30 can also be simplified in its structure since it does not use a final reduction gear and the like as power transmission means.
However, the driving rod 36 is fixed in length and thus the length of the barrel is not adjustable, which makes it difficult to miniaturize the device. A driving circuit is also sophisticated since a driving signal is provided as an asymmetric waveform in place of sine wave.
There are rising demands for a lens transfer device which can be installed in a small volume, be controlled precisely with high transfer resolution, and produce a sufficient displacement for transfer with a small amount of driving force